Vacuum tube keying of resistance coupling amplifier



y 9, 1952 QB. COLEMAN 2,605,402

VACUUM TUBE KEYING OF RESISTANCE COUPLING AMPLIFIER Filed May 20, 1950Multiplier Source of Oscillation 33 9.

. 8+ Amplifier i- -L- B'.;O 4.

39 4 3 4| 2; 3 1| v 9 r: 7 :2 2 5 I 255 45 37 Kyer wmusssss: INVENTORClorence B. co lerncm.

.provide a keyer. which; shallproduce sharply Patented July 29, 1952 v YL 2,605,402. 7 v v VAC UM TUBE KEYING; F RESISTANCE i COUPLING UClarence B. Coleman, Baltimore, MIL, assignor to westinghouse Electric,Corporation, ;East Pittsburgh,.Pa., a corporation of PennsylvaniaApplication MayZO, 1950, Serial No.1sa294 My invention relates toelectric discharge appa- 9 Claims. (01.25%5271 V ratus and it hasparticular relation to electronic keyers. v -The Usselman Patent2,153,656 is illustrative 'ofkeyers of the prior art ofwhic'h I amaware.

Such'keyers include one or more pentodes.' ,Oscillationsiderived from.an exciter are impressed between: the control grids and the cathodes,and

keying potential is impressed between the sup- 'pressor grids and thecathodes of the pentodes.

The anodes of the pentodes'are coupled to'the control grids of followingamplifiers. keying potential is:varied, the pentodes pass from As thesubstantially conductive to a substantially-non- .conductive condition.During theintervalswhen the. pentodes are conductive, trains ofoscillations derivedxfro'm the exciter are impressed on the -followingamplifiers.

The variations in the pentode conductivity. are thus impressed asmodulations-on :oscill'ations derived from the excite'r source. Thesignals transmitted when the pentodes are non-conductive may bedesignated as marksignals .and the signals transmitted when the-pentodesare conductive may be designated as gap signals. .iToachieve precisionin signalling,v -it;is essential that the mark and: gap intervals besharply defined; it is desirable then, that the trains of oscillationsbe initiated and terminated abruptly.

I have, found'that prior art keyersihave the serious disadvantage. :thatthe marksgap modulations are not sharplydefined. The transmitted signalappears to pass gradually-between:the='gap magnitude to the. markmagnitude; 5

i "It is, accordingly,-, an pbjejct of my invention to fined mark-gapsignals.

A more specific object of my invention is to provide akeyercapacitively. coupled to follow .ing amplifying stages which shallproduce sharpx1y defined;mark-gap signals.- v

'An auxiliary object of my invention is .toprovide a novel pentodecircuit;

' My invention arises from therealization that the bluntness in themark-gap signals is caused by the lag inthe reference to the keyingvariations of the coupling network between the keyed pentode and .theamplifiers. "This network may include'a coupling capacitor whichis'cliarged and discharged as the conductivity of 'the'key'e'd pentodeis varied by the keying oscillations. When the keyed pentode issubstantially nonconductive, its anode and therefore'one plate or thecoupling capacitor are substantially at the positivepotential of thesupply. The coupling capacitor is, thereforegg; charged to the potentialof the supply. When the keyed pentode becomes conductive, the potentialof the above-specified plate T of :the, coupling capacitor I issubstantially reduced andrthev capacitor tends to discharge.

.As the keying potentialis varied, the D. C. po-

tentialifrom the platesupply impressed on the capacitor lthus. varies inrhythm with the keying variation.=, Inefiect, then the oscillations fromthe .exciter are modulated, not'by a potential having the precise waveform of the keying potential, but by one having the wave form producedby thecharge and discharge of the capacitor. The

sharpness of this modulation is materiallylimited by thetimerequired,for the capacitor to discharge. 'Ihistime interval is, in turn,dependent on the resistance in the discharging circuit of the capacitorand sincethis resistance is substantial,

the rise and drop of the grid potential of the follcwving amplifier isrelatively-gradual and the mark and gap signals are not sharply definedas is desirable. v =;In accordance with specific objects of myinvention, I provide a'pairof pentodes on the suppressor grids of whichthe keying signal is impressed-and the screen grid of each of which isconnected; to the anode of the other. The anode of one of the keyertubes is capacitatively coupled to the grid of the following-amplifier.it is a property of-a pentodethat as the suppressor gridpotentialisvaried, the total current drawn fromthecathode-by the screen gridandthe anode remains. constant The variation in one senseotthe currentflowing to the anode is compensated by corresponding variations in theopposite sense of.- current-fiowing to the screen grid.

.As-the current flow to the anode coupled to the amplifier varies; byreason of the keying variations, the -current flow to the screen grid ofthe other time yariesin such manner as to compensate .-for the formervariations. The charge on thecoupling capacitor, therefore, remainssubstantially constant and the conductivity of the amplifier to whichthe keye'r is coupled is varied sharply. Themark gap modulations are,therefore, sharply distinguishable.

The novelfeatures that I consider characteristicofmy invention are setforth with particularityw n the appended claims. The invention.itself,-'"however, both as to its organization and its methodofoperation, together with additional objects and advantages thereof willbe understood from the following description of a specific'embodimen'twhenread in connection with the accompanying drawing inwhich the single figure 3 is a circuit diagram of a preferred embodimentof my invention.

The apparatus shown in the drawing includes a first pentode I having ananode 3, a cathode 5, a control grid 1, a screen grid 9 and a suppressorgrid II; and a second pentode I3 having similar electrodes I5, I'I, I9,2I and 23 respectively' The anodes are suppliedfrom a suitable B supply(not shown) through load resistors 24 and 25. The cathodes and I! aregrounded through cathode resistors 26 and 21 respectively and by-passedby by-pass capacitors 29 and 3I respectively of suit able magnitude. Theoutput of an oscillator 33 preferably of the CW type isv impressedbetween the control grid 1, and the cathode 5 of the'first pentode Ithrough a grid resistor 35'. The sup- Grid resistor 45 of amplifier 43 Bpotential Keyer output potential pressor grids II and 23 respectively,are con- 1 nected together to the output of a keyer 31. The screen grid9 and 21 of each pentode I and I3 respectively is connected directly orthrough a connection having substantially no impedance to the anode I5and 3-of theother. I

The keyer 31 maybe of any well knowntype.

In the preferred practice of my invention, it supplies alternativelynegative potentials of such magnitude that when they are impressed onthe suppressor grids II and 23 the pentodesI and I3 are non-conductiveand positive potentials. of

such magnitude that when they are impressed on the suppressor gridsfthepentodes I and I3 are substantiallyconductive. Y

The anode'3 of the first pentode I is coupled through a-capacitor' 39'to the control grid M of a following amplifier 43. The latter grid'dlmay be grounded through a grid resistor 45. Theoutput of theamplifier 43may be coupled through frequency multipliers and output amplifiers 41which may be, in turn; coupled to an antenna 49 1 of acommunicationline. r Y

I have found that as a potential is supplied by the ,keyer, a signalhaving sharp mark and gap modulations is transmitted. When the keyerpotential is negative, the anode current of both pentodes I and I3is'substantially zero. However,

the screen gridZI of the second pentode I3 draws current substantiallyequal to the current drawn by the anode I5 of this pentode (andtherefore, by the anode'f3 of the pentode I) when it is fully conductiveand, therefore, the direct current drawn from the B -supply rem'ainsunchanged. While thefirst pentod I is non-conductive,-the

carrier oscillations impressed on its control grid are not transmittedthrough the coupling capa'citor, therefore, these oscillations are nottransmitted through the amplifier to the antenna.

When the potential derived from the keyer 31 is positive 'or'at suchother magnitude as to render the first pentode l conductive, the D. C.current drawnfrom' the'supply remains unchanged.

'Ho'wever; the oscillations impressed from th'e'osvI clllator (i3 arenow impressed through the coupling capacitor 39 on the amplifier 43 andtransmitted'by the antenna 49.

'In the practice of my invention, the coupling capacitor 39 may also beconnected to the anode pacitor 39 connected with the anode of the firstpath 1 i In a system in accordance with my invention which I have foundto operate satisfactorily, the following components are included:

Load resistor 25 of second pentode 13 51.000 ohm Cathode resistor 26 offirst pentodenu- 1.200 ohm Cathode resistor 27 of second pentode; 1.200ohm By-pass capacitor 28 of first pent0de 0:1 mf. By-pass capacitor 31of second pentode 0.1 mt. Grid resistor 35 of first pentode 51.000 ohmCoupling capacitor 39 0 1 mf. 100.000 ohm 250 Oscillator (33) potential1 volt R. M. S.

While in accordance with the specific aspects of my invention a pair ofpentodes I and I3 are included in the keying system, occasions may arisein which tubes of other types are applicable. For example, the pentodesmay be included in a single envelope or a pair of pentagrid convertersproperly connected may have the properties necessary in the practice ofmy invention andmay be utilized. Under certain circumstances thecapacitive coupling 39 may be replaced by an inductive coupling; acoupling transformer, for example. To th extent that the basic conceptsof my invention are applied to such an inductively coupled system, suchsystem lies within the scope of my invention. Under certaincircumstances the keyer and control potentials may be distributeddifierently among the grids of the pentodes.

than in the specific system illustrated. Such different distributionlies Wtihin the scope of the broad aspects of my invention.

My, invention is herein shown as applied to the keying of radiofrequency oscillations. Itis also, applicable. to the keying of audiofrequency oscillations. For example, the keyerin accordance with myinvention may be connected to key the modulator'of a transmitteroperating by transmitting .AM or FM modulated continuous waves. v i.While Ihave shown and described a specific embodiment of my invention,many modifications thereof are possible. My invention, therefore, is notto be restricted except insofar as is necessitated by the prior art andby the spirit of the appended claims.

I claim as my invention: l. A keying circuit including a pair ofpentodes and a network for impressing keying potentials simultaneouslyon the suppressor grids of said pentodes characterized. by the fact thatthe screen grid of each of said pentodes is connected to' the anode ofthe other" of said pentodes through a connection having substantially noimpedance.

2. In combination, a first electric discharge path defined by. an anodeand a cathode and ineluding-"a control grid; a screen grid and asuppressor grid; connections for impressing a signal on s'aidcontrolgrid; a "second electric discharge path defined by an anode and acathode and also including a control grid, a screen grid and asuppressor grid; a connection between said last-named'control grid .andcathode; a keying network; connections for impressing the output of saidkeying network on both said suppressor grids; a connection betweenthescreen gridof each of said paths and the anode of the other of saidpaths; and an output connection including a coupling capacitor connectedto the anode of one of said paths. 1

3. 1m combination, a first electric discharge path defined by an anodeand a cathode and including a control grid, a screen grid and asuppressor grid; a second electric discharge path defined by an anodeand a cathode and also including a control grid, a screen grid and asuppressor grid; a keying network; connections for impressing the outputof said keying network on said suppressor grids; a connection betweenthe screen grid of each of said paths and the anode of the other of saidpaths; and an output connection including a coupling capacitor connectedto the anode of one of said paths. v

4. In combination, a first electric discharge path defined by an anodeand a cathode and including a control grid, a screen grid and asuppressor grid; a second electric discharge path defined by an anodeand a cathode and also including a control grid; a screen grid and asuppressor grid; a network for impressing control potentials on saidsuppressor grids; a connection between the screen grid of each of saidpaths and the anode of the other of said paths; and an output connectionincluding a coupling capacitor connected to the anode of one of saidpaths.

5. In combination, a first electric discharge path defined by an anodeand a cathode and including a control grid, a screen grid and asuppressor grid; a second electric discharge path defined by an anodeand a cathode and also including a control grid, a screen grid and asuppressor grid; a connection of substantially no impedance between thescreen grid of each of said paths and the anode of the other of saidpaths; and an output connection connected to the anode of one of saidpaths.

6. In combination, a first electric discharge path defined by an anodeand a cathode and including a control grid, a screen grid and asuppressor grid; connections for impressing a signal on said controlgrid; a second electric discharge path defined by an anode and a cathodeand also including a control grid, a screen grid and a suppressor grid;a connection between said lastnamed control grid and cathode; a keyingnetwork adapted to supply as an output alternatively a first potentialwhich when impressed on the suppressor grid of either of said paths issuflicient to reduce the conductivity of said path to a low magnitude ora second potential which when impressed on the suppressor grid of eitherof said paths is sufiicient to render said path substantiallyconductive; connections for impressing the output of said keying networkon both said suppressor grids; a connection between the screen grid ofeach of said paths and the 6 anode of the other of said paths; and anoutput connection including a coupling capacitor connected to the anodeof one of said paths. 7

'7. In combination, a first electric discharge path defined by ananodeand a cathode and including a control grid, a screen grid and asuppressor grid; a second electric discharge path defined by an anodeand a cathode and also including a control grid, a screen grid and asuppressor grid; connections between said control grids and theirassociated cathodes, respectively; a keying network; connections forimpressing the output of said keying network on said suppressor grids, aconnection between the screen grid of each of said paths and the anodeof the other of said paths; and an output connection including acoupling capacitor connected to the anode of one of said paths.

8. In combination, a first electric discharge path defined by an anodeand a cathode and including a control grid, a screen grid and asuppressor grid; 9. second electric discharge path defined by an anodeand a cathode and also including a control grid, a screen grid and asuppressor grid; connections between said control grids and theirassociated cathodes respectively; a connection between the screen gridof each of said paths and the anode of the other of said paths; and anoutput connection connected to the anode of one of said paths.

9. In combination, a first electric discharge path defined by an anodeand a cathode and having a plurality of grids; a second discharge pathdefined by an anode and a cathode and also having a plurality of grids;a keyer; connections for impressing the output of said keyer oncorresponding first grids of each of said paths; connections forimpressing a signal on a second grid of said first path; connectionsbetween a second grid of. said second path corresponding to said secondgrid of said first path and said cathode CLARENCE B. COLEMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED-STATES PATENTS Name Date De Rosa May 25, 1948 Number

